1. Field of the Invention
The present invention relates to a printing method, a printing apparatus, a computer-readable medium, and a correction pattern.
2. Description of the Related Art
Some inkjet printers, which perform printing by making a print head eject ink while making it move bidirectionally in a main-scanning direction, have a so-called “bidirectional printing” function which enables printing by ejecting ink during both the forward pass and return pass of the print head.
In performing the bidirectional printing, it is necessary to correct the positions at which dots are formed, in the main-scanning direction, by ink drops ejected during the forward pass and the return pass.
A correction amount for correcting the dot-formation positions may be determined, for example, as follows:
First, while printing during the forward pass, nozzles at the leading edge (in the main-scanning direction) of the print head are used to print, at a predetermined interval in the main-scanning direction, several vertical lines that extend in the sub-scanning direction (sheet-carrying direction). Vertical lines are printed also during the return pass, but when printing the lines during the return pass, different correction amounts are added to each predetermined interval between the lines used in the forward pass, so that the same number of lines are printed but with slightly different intervals between each. Using the pattern printed in this way, the correction amount for bidirectional printing is determined by making a user etc. select a line printed during the forward pass and a line printed during the return pass that look closest to a straight line, and adopting the correction amount that has been added when printing the selected line.
In order to print images having the quality of film-camera photographs, some inkjet printers not only use inks of the four colors—cyan, magenta, yellow, and black—that are necessary for printing in color, but also use additional colors of inks such as light-colored inks (i.e., light cyan ink and light magenta ink) and also dark yellow ink to perform printing with, for example, a total of seven colors of inks. On the other hand, when printing illustrations that only require a limited number of colors for color printing, the light cyan ink, the light magenta ink, and the dark yellow ink are not used because only inks of the four colors, cyan, magenta, yellow, and black, need to be used. In view of such circumstances, some recent inkjet printers—which have seven print heads on which independent cartridges each containing ink of different colors can be detachably mounted—are capable of using ink cartridges of seven colors when printing high-quality images, and also capable of holding ink cartridges each containing cyan ink, magenta ink, and yellow ink, instead of the ink cartridges containing the light cyan ink, the light magenta ink, and the dark yellow ink, and using two print heads for each color for printing when it is desired to print at a higher speed.
When printing is performed using the four colors of inks, ink of the same color is mounted on two print heads. Therefore, as for the two print heads that eject ink of the same color, it becomes necessary to correct the positions at which dots are formed, in the main-scanning direction, by ink drops ejected during the forward pass and the return pass. On the other hand, when printing is performed using the seven colors of inks, it is preferable to correct the positions at which dots are formed, in the main-scanning direction, by ink drops ejected during the forward pass and the return pass for print heads ejecting light-colored inks, particularly, the print head ejecting light cyan ink and the print head ejecting light magenta ink.
Therefore, it is necessary to set independently a correction value for printing with the seven colors and a correction value for printing with the four-colors as the correction values for correcting the positions at which dots are formed in the main-scanning direction by ink drops ejected during the forward pass and the return pass. More specifically, in order to determine the correction value for the seven-color print mode and the correction value for the four-color print mode, it is necessary to print two types of correction patterns using different print heads for each print mode. This requires twice the printing time and ink consumption.